1. Field of the Invention
The present invention relates to a disc brake system of floating caliper type.
2. Description of Related Art
FIG. 7 shows a floating caliper disc brake system disclosed in Japanese Patent Utility Model 57-144631. Referring to FIG. 7, a disc 1 rotates integrally with a wheel and a mounting 2 (mount) which acts as a torque member is secured to a vehicle body. A caliper body 3 is also provided. The mounting 2 is provided with a pair of arms 2A, 2B across the disc, which are apart from each other in the peripheral direction of the disc 1.
The caliper body 3 is provided with an inner portion 3A and an outer portion 3B and disposed across an inner pad 4 and an outer pad 5 which interpose the disc 1. The inner portion 3A is provided with a cylinder 6 for slidably accommodating a piston 7 through a piston seal 8. The piston 7 presses the inner pad 4 against the disc 1.
The caliper body 3 has pin securing portions 10A, 10B which are disposed in a disk outlet portion (a portion from where the rotating disc is moved away from the pad) and a disk inlet portion (a portion from which the rotating disc is moved toward the pad). Base portions of slide pins 11, 12 disposed in parallel with a direction perpendicular to the disc 1 are connected to the pin securing portions 10A, 10B. An arrow P indicates a rotational direction of the disc 1 during forward movement of the vehicle. When the two slide pins 11, 12 are slidably inserted into guide holes 13, 14 formed in the arms 2A, 2B of the mounting 2 respectively, the caliper body 3 is supported in a floating state in a direction perpendicular to the disc 1.
In the foregoing case, a base portion of the slide pin 11 is firmly joined to the pin securing portion 10A at the disc outlet portion with a bolt. A pin engagement groove 16 having an opening facing the disc inlet portion is formed in the pin securing portion 10B at the disc inlet portion. The slide pin 12 is held by an elastic anchoring member 17 in a state where cylindrical base portion 12a of the slide pin 12 is fitted in the pin engagement groove 16. Thus, the slide pin 12 is allowed to be rotated only in the rotational direction of the disc.
In the above-structured disc brake system, when the inner pad 4 is pressed against the disc 1 by the piston 7, reaction force is generated so that the caliper body 3 is guided by the slide pins 11, 12 and the guide holes 13, 14 respectively for a sliding motion. Thus, the caliper body 3 presses the outer pad 5 against the disc 1 so as to interpose the disc 1 together with the inner pad 4, thus generating braking force. When the pressure applied by the piston 7 is released, the piston seal 8 serves to retract the caliper body 3 to an initial position.
In order to reliably obtain the braking force from the disc brake system having the slide pin type guide as described above, the slide pin is required to smoothly slide in the guide hole in the direction perpendicular to the disc. Therefore, the clearance between the slide pins and the guide holes has to be set to a relatively large value, allowing for the influence of machining tolerances and the like. However, the portion between the slide pins and the guide holes is likely to get warped during braking operation. As a result, the caliper body cannot easily be retracted to the initial position even after the pressure has been removed, resulting in dragging.
In order to overcome the above-described drawback, the disc brake system has a structure in which the slide pin 12 is connected to the pin securing portion 10B such that the slide pin 12 is allowed to move only in the rotational direction of the disc. However, the above-mentioned structure cannot sufficiently absorb the machining tolerances between the slide pins 11, 12 and the guide holes 13, 14 respectively. Therefore, the clearance between the slide pins and the guide holes has not been set to a substantially small value.